Passive Cooling Strategies - Low Energy Cooling for Sustainable Buildings - page 64

if the room temperature is below 22 ◦ C, that is, too cool. Otherwise the earth heat
exchanger is always used during summer operation of the building, regardless of soil
temperature. This can have the effect that unwanted gains can occur using the heat
exchanger, if outside temperatures are lower than the soil temperature. A better control
strategy would be to compare inlet air and soil temperature in summer to prevent heat
input.
3.1.2 Rehabilitated Office Building in Tubingen
The passive energy office building in Tubingen has been rehabilitated and is now
occupied by the engineering company ebok and is part of a former military barse
called the Thiepval Barracks (see Figure 3.3).
Roof and wall insulation (30 cm and 24 cm thick) and triple-glazed windows with a
U -value of 0 . 8Wm − 2 K − 1 correspond to passive house standards. The floor insulation
in the existing building is only 7 . 5 cm due to low ceiling heights so that a low cost
perimeter insulation had to be chosen to prevent excessive ground losses. The building
has a useful heated floor area of 833m 2 and a gross room volume of 3724m 3 .Itis
mechanically ventilated with winter heat recovery and summer precooling of the
ambient air through a brine-based, ground-coupled heat exchanger installed around
the building perimeter. A natural ventilation concept was difficult to implement due
to the low height of the building, resulting security problems with window openings
and restrictions due to the protection of listed buildings. Therefore the mechanical
ventilation system was sized to provide up to 4000 m 3 h − 1 (about two air changes)
for night ventilation at a low pressure drop. The specific electricity consumption for
night ventilation is a total of 0 . 48Wm − 3 h for both the supply and exhaust fan. This
compares with the daytime ventilation with a reduced volume flow of 2000 m 3 h − 1
and a total electricity demand for the two fans of 0 . 17Wm − 3 h.
Figure 3.3 Rehabilitated passive standard office building in Tubingen, Germany